An envelope defines the loudness profile of a particular sound, in conjunction with the sound's level. All sounds must have a corresponding envelope to be listenable.
An envelope has a name, a profile curve, an attack duration and a release duration, which are defined in seconds.
The profile curve is a piecewise-linear function, whose values range between 0 and 1. This function is stretched horizontally to fit the length of the sound it is assigned to, so as to define a full loudness profile for any sound duration. At the locations where the envelope's value is 0, the sound is output with a level of 0 (it is silent). At the locations where the envelope's value is 1, the sound is output at the sound's current level value. At intermediate values between 0 and 1, the sound's output level is linearly interpolated between 0 and the sound's current level.
The horizontal stretching (mapping on the sound's duration) is linear if both attack and release are set to 0. Otherwise, if the attack is non-zero, the first 3rd portion of the curve profile is mapped to the exact attack duration (i.e., the portion of the curve between 0 and 1/3 will be mapped to last exactly the attack time). The converse can be applied to the release time and the last 3rd of the curve. Then, the rest of the curve (the portion [1/3-2/3] is stretched so as to match the remaining duration of the sound (i.e. the sound's duration minus the attack and release times).
If the sound duration is shorter than the sum of the attack and release time, then those (attack and release) are treated as if they were 0 (i.e. the full profile is mapped onto the full sound duration).
The envelopes editor lets you select a current envelope that is applied to newly created sounds and can be assigned to selected sounds. The envelope editor also lets you create new envelopes, edit or delete existing envelopes. The current envelope and its name is shown at the top of the envelope editor, while the list below shows all available envelopes.
Envelopes and modulation: note that envelopes can be modulated, to produce either tremolo or ring modulation effects, through modulation curves.